Five siblings expand the spectrum of GPC6-related skeletal dysplasia.

Skeletal dysplasias broadly include disorders of cartilage or bone. Omodysplasia-1 is a type of skeletal dysplasia caused by biallelic loss of function variants in the GPC6 gene. GPC6 codes for the protein glypican 6 (GPC6) (OMIM *604404), which stimulates bone growth. We report a family in which five out of nine children were presented with a skeletal dysplasia characterized phenotypically by mild short stature and rhizomelia. All affected individuals were found to have homozygous missense variants in GPC6: c.511 C>T (p.Arg171Trp). Radiograph findings included rhizomelic foreshortening of all four extremities, coxa breva, and ulna minus deformity. Using a Hedgehog (Hh) reporter assay, we demonstrate that the variant found in this family results in significantly reduced stimulation of Hh activity when compared to the wild-type GPC6 protein, however protein function is still present. Thus, the milder phenotype seen in the family presented is hypothesized due to decreased GPC6 protein activity versus complete loss of function as seen in omodysplasia-1. Given the unique phenotype and molecular mechanism, we propose that this family's findings widen the phenotypic spectrum of GPC6-related skeletal dysplasias.

Glypican-6 and Glypican-4 stimulate embryonic stomach growth by regulating Hedgehog and noncanonical Wnt signaling.

BACKGROUND: Glypicans are a family of proteoglycans that play important roles in embryonic morphogenesis. The mammalian genome contains six glypicans (GPC1 to GPC6). GPC6 and GPC4 are the pair of glypicans that show the highest degree of homology within the family. GPC6-null embryos display bone abnormalities and severely shortened intestines. RESULTS: We show that GPC6-null embryos display significantly smaller stomachs, and that Hedgehog and noncanonical Wnt signaling are dysregulated in GPC6-null stomachs. Like GPC6, GPC4 is expressed by the developing stomach. However, GPC4-null embryos have normal stomachs. To investigate whether GPC6 and GPC4 display functional overlap in the developing stomach, we crossed GPC4-null mice with GPC6 conditional mutants in which the expression of this glypican is severely reduced in the stomach. Notably, we found that the compound mutants display stomachs that are smaller than those of the GPC6 conditional mutants. We also found that this functional overlap between GPC6 and GPC4 is mediated by the noncanonical Wnt pathway. CONCLUSION: This study demonstrates that GPC6 stimulates the growth of the embryonic stomach via Wnt and Hh signaling. In addition, we uncovered a Wnt-mediated functional overlap between GPC6 and GPC4 in the developing stomach.

The function of glypicans in the mammalian embryo.

Glypicans are proteoglycans that are bound to the outer surface of the plasma membrane by a glycosylphosphatidylinositol anchor. The mammalian genome contains six members of the glypican family (GPC1 to GPC6). Although the degree of sequence homology within the family is rather low, the three-dimensional structure of these proteoglycans is highly conserved. Glypicans are predominantly expressed during embryonic development. Genetic and biochemical studies have shown that glypicans can stimulate or inhibit the signaling pathways triggered by Wnts, hedgehogs, fibroblast growth factors, and bone morphogenetic proteins. The study of mutant mouse strains demonstrated that glypicans have important functions in the developmental morphogenesis of various organs. In addition, a role of glypicans in synapsis formation has been established. Notably, glypican loss-of-function mutations are the cause of three human inherited syndromes. Recent analysis of glypican compound mutant mice has demonstrated that members of this protein family display redundant functions during embryonic development.

Processing by convertases is required for glypican-3-induced inhibition of Hedgehog signaling.

Glypican-3 (GPC3) is one of the six members of the mammalian glypican family. We have previously reported that GPC3 inhibits Hedgehog (Hh) signaling by competing with Patched (Ptc) for Hh binding. We also showed that GPC3 binds with high affinity to Hh through its core protein, but that it does not interact with Ptc. Several members of the glypican family, including GPC3, are subjected to an endoproteolytic cleavage by the furin-like convertase family of endoproteases. Surprisingly, however, we have found that a mutant GPC3 that cannot be processed by convertases is as potent as wild-type GPC3 in stimulating Wnt activity in hepatocellular carcinoma cell lines and 293T cells and in promoting hepatocellular carcinoma growth. In this study, we show that processing by convertases is essential for GPC3-induced inhibition of Hh signaling. Moreover, we show that a convertase-resistant GPC3 stimulates Hh signaling by increasing the binding of this growth factor to Ptc. Consistent with this, we show that the convertase-resistant mutant binds to both Hh and Ptc through its heparan sulfate (HS) chains. Unexpectedly, we found that the mutant core protein does not bind to Hh. We also report that the convertase-resistant mutant GPC3 carries HS chains with a significantly higher degree of sulfation than those of wild-type GPC3. We propose that the structural changes generated by the lack of cleavage determine a change in the sulfation of the HS chains and that these hypersulfated chains mediate the interaction of the mutant GPC3 with Ptc.

Insights into the key roles of proteoglycans in breast cancer biology and translational medicine.

Proteoglycans control numerous normal and pathological processes, among which are morphogenesis, tissue repair, inflammation, vascularization and cancer metastasis. During tumor development and growth, proteoglycan expression is markedly modified in the tumor microenvironment. Altered expression of proteoglycans on tumor and stromal cell membranes affects cancer cell signaling, growth and survival, cell adhesion, migration and angiogenesis. Despite the high complexity and heterogeneity of breast cancer, the rapid evolution in our knowledge that proteoglycans are among the key players in the breast tumor microenvironment suggests their potential as pharmacological targets in this type of cancer. It has been recently suggested that pharmacological treatment may target proteoglycan metabolism, their utilization as targets for immunotherapy or their direct use as therapeutic agents. The diversity inherent in the proteoglycans that will be presented herein provides the potential for multiple layers of regulation of breast tumor behavior. This review summarizes recent developments concerning the biology of selected proteoglycans in breast cancer, and presents potential targeted therapeutic approaches based on their novel key roles in breast cancer.

Glypican-3 binds to Frizzled and plays a direct role in the stimulation of canonical Wnt signaling.

Glypican-3 (GPC3) is a proteoglycan that is bound to the cell surface. It is expressed by most hepatocellular carcinomas (HCCs) but not by normal hepatocytes. GPC3 stimulates HCC growth by promoting canonical Wnt signaling. Because glypicans interact with Wnts, it has been proposed that these proteoglycans stimulate signaling by increasing the amount of Wnt at the cell membrane, thus facilitating the interaction of this growth factor with its signaling receptor, Frizzled. However, in this study, we demonstrate that GPC3 plays a more direct role in the stimulation of Wnt signaling. Specifically, we show that, in addition to interacting with Wnt, GPC3 and Frizzled interact directly through the glycosaminoglycan chains of GPC3, indicating that this glypican stimulates the formation of signaling complexes between Wnt and Frizzled. Consistent with this, we show that the binding of Wnt at the cell membrane triggers the endocytosis of a complex that includes Wnt, Frizzled and GPC3. Additional support for our model is provided by the finding that glypican-6 (GPC6) inhibits canonical Wnt signaling, despite the fact that it binds to Wnt at the cell membrane.

LRP1 mediates Hedgehog-induced endocytosis of the GPC3-Hedgehog complex.

Glypican-3 (GPC3) is a heparan sulfate (HS) proteoglycan that is bound to the cell membrane through a glycosylphosphatidylinositol link. This glypican regulates embryonic growth by inhibiting the hedgehog (Hh) signaling pathway. GPC3 binds Hh and competes with Patched (Ptc), the Hh receptor, for Hh binding. The interaction of Hh with GPC3 triggers the endocytosis and degradation of the GPC3-Hh complex with the consequent reduction of Hh available for binding to Ptc. Currently, the molecular mechanisms by which the GPC3-Hh complex is internalized remains unknown. Here we show that the low-density-lipoprotein receptor-related protein-1 (LRP1) mediates the Hh-induced endocytosis of the GPC3-Hh complex, and that this endocytosis is necessary for the Hh-inhibitory activity of GPC3. Furthermore, we demonstrate that GPC3 binds through its HS chains to LRP1, and that this interaction causes the removal of GPC3 from the lipid rafts domains.

Combined genetic-pharmacologic inactivation of tightly linked ADAMTS proteases in temporally specific windows uncovers distinct roles for versican proteolysis and glypican-6 in cardiac development.

Extracellular matrix remodeling mechanisms are understudied in cardiac development and congenital heart defects. We show that matrix-degrading metalloproteases ADAMTS1 and ADAMTS5, are extensively co-expressed during mouse cardiac development. The mouse mutants of each gene have mild cardiac anomalies, however, their combined genetic inactivation to elicit cooperative roles is precluded by tight gene linkage. Therefore, we coupled Adamts1 inactivation with pharmacologic ADAMTS5 blockade to uncover stage-specific cooperative roles and investigated their potential substrates in mouse cardiac development. ADAMTS5 blockade was achieved in Adamts1 null mouse embryos using an activity-blocking monoclonal antibody during distinct developmental windows spanning myocardial compaction or cardiac septation and outflow tract rotation. Synchrotron imaging, RNA in situ hybridization, immunofluorescence microscopy and electron microscopy were used to determine the impact on cardiac development and compared to Gpc6 and ADAMTS-cleavage resistant versican mutants. Mass spectrometry-based N-terminomics was used to seek relevant substrates. Combined inactivation of ADAMTS1 and ADAMTS5 prior to 12.5 days of gestation led to dramatic accumulation of versican-rich cardiac jelly and inhibited formation of compact and trabecular myocardium, which was also observed in mice with ADAMTS cleavage-resistant versican. Combined inactivation after 12.5 days impaired outflow tract development and ventricular septal closure, generating a tetralogy of Fallot-like defect. N-terminomics of combined ADAMTS knockout and control hearts identified a cleaved glypican-6 peptide only in the controls. ADAMTS1 and ADAMTS5 expression in cells was associated with specific glypican-6 cleavages. Paradoxically, combined ADAMTS1 and ADAMTS5 inactivation reduced cardiac glypican-6 and outflow tract Gpc6 transcription. Notably, Gpc6-/- hearts demonstrated similar rotational defects as combined ADAMTS inactivated hearts and both had reduced hedgehog signaling. Thus, versican proteolysis in cardiac jelly at the canonical Glu441-Ala442 site is cooperatively mediated by ADAMTS1 and ADAMTS5 and required for proper ventricular cardiomyogenesis, whereas, reduced glypican-6 after combined ADAMTS inactivation impairs hedgehog signaling, leading to outflow tract malrotation.

Overgrowth of a mouse model of Simpson-Golabi-Behmel syndrome is partly mediated by Indian hedgehog.

Loss-of-function mutations of Glypican 3 (Gpc3) cause the Simpson-Golabi-Behmel overgrowth syndrome (SGBS), and developmental overgrowth is observed in Gpc3-null mice, a mouse model for SGBS. We recently reported that GPC3 inhibits Hedgehog (Hh) signalling by inducing its endocytosis and degradation. Here, we show that the developmental overgrowth observed in Gpc3-null mice is, at least in part, a consequence of the hyperactivation of the Hh pathway. We bred Gpc3-null mice with mice that are Hh signalling-deficient owing to the lack of Indian Hh (Ihh), one of the three mammalian Hhs. We found that the Gpc3-null mice showed a 29.9% overgrowth in an Ihh wild-type background, whereas an Ihh-null background partly rescues the overgrowth caused by the lack of Gpc3 as the double mutants were 19.8% bigger than the Ihh-null mice. Consistent with the role of GPC3 in Hh endocytosis and degradation, the Gpc3-null mice show increased levels of Ihh protein and signalling, but similar levels of Ihh messenger RNA.

Soluble glypican 3 inhibits the growth of hepatocellular carcinoma in vitro and in vivo.

The heterogeneity of the molecular pathology of HCC poses a formidable obstacle to the development of non-cytotoxic therapies. Several pro-tumorigenic signaling pathways can be aberrantly activated in HCC, including those triggered by Wnts. Glypican-3 (GPC3), a membrane-bound heparan sulfate proteoglycan that is overexpressed in most HCCs, promotes the growth of these tumors by stimulating Wnt signaling. Because GPC3 binds with high affinity to Wnts, and its growth-promoting activity requires attachment to the cell membrane, we have hypothesized that a mutated GPC3 lacking the GPI anchoring domain (sGPC3) will block Wnt signaling and inhibit the growth of Wnt-dependent tumors. In addition, because sGPC3 displays heparan sulfate chains, this secreted glypican could also inhibit HCC growth by blocking the activity of other heparin-binding growth factors. To test this hypothesis, HCC cell lines were infected with an sGPC3-expressing lentivirus or virus control, and the effect of sGPC3 on the in vitro and in vivo growth was investigated. In addition, the signaling pathways targeted by sGPC3 were identified. We observed that sGPC3-expressing cells had lower proliferation rate. In addition, sGPC3 significantly inhibited the in vivo growth of the Huh6, HepG2 and Huh7 HCC cell lines. sGPC3 blocked Wnt signaling in Huh6- and Huh7-derived tumors and Erk1/2 and Akt phosphorylation in tumors generated by Huh7 and HepG2 cells, respectively. An anti-angiogenic effect in Huh7 and HepG2-derived tumors was also observed. We conclude that sGPC3 can inhibit HCC tumorigenicity by blocking the activity of several pro-tumorigenic growth factors.

Glypican-6 stimulates intestinal elongation by simultaneously regulating Hedgehog and non-canonical Wnt signaling.

We report here that Glypican-6 (GPC6)-null mice display at birth small intestines that are 75% shorter than those of normal littermates. Notably, we demonstrate that the role of GPC6 in intestinal elongation is mediated by both Hedgehog (Hh) and non-canonical Wnt signaling. Based on results from in vitro experiments, we had previously proposed that GPC6 stimulates Hh signaling by interacting with Hh and Patched1 (Ptc1), and facilitating/stabilizing their interaction. Here we provide strong support to this hypothesis by showing that GPC6 binds to Ptc1 in the mesenchymal layer of embryonic intestines. This study also provides experimental evidence that strongly suggests that GPC6 inhibits the activity of Wnt5a on the intestinal epithelium by binding to this growth factor, and reducing its release from the surrounding mesenchymal cells. Finally, we show that whereas the mesenchymal layer of GPC6-null intestines displays reduced cell proliferation and a thinner smooth muscle layer, epithelial cell differentiation is not altered in the mutant gut.

Assembling custom side chains on proteoglycans to interrogate their function in living cells.

Proteoglycans (PGs) are composed of a core protein and one or more chains of glycosaminoglycans (GAGs). The highly heterogeneous GAG chains play an irreplaceable role in the functions of PGs. However, the lack of an approach to control the exact structure of GAG chains conjugated to PGs tremendously hinders functional studies of PGs. Herein, by using glypican-3 as a model, we establish an aldehyde tag-based approach to assemble PGs with specific GAG chains on the surface of living cells. We show that the engineered glypican-3 can regulate Wnt and Hedgehog signaling like the wild type. Furthermore, we also present a method for studying the interaction of PGs with their target glycoproteins by combining the assembly of PGs carrying specific GAG chains with metabolic glycan labeling, and most importantly, we obtain evidence of GPC3 directly interacting with Frizzled. In conclusion, this study provides a very useful platform for structural and functional studies of PGs with specific GAG chains.

Glypican-3 regulates migration, adhesion and actin cytoskeleton organization in mammary tumor cells through Wnt signaling modulation.

Glypican-3 (GPC3) is a proteoglycan involved in migration, proliferation and cell survival modulation in several tissues. There are many reports demonstrating a downregulation of GPC3 expression in some human tumors, including mesothelioma, ovarian and breast cancer. Previously, we determined that GPC3 reexpression in the murine mammary adenocarcinoma LM3 cells induced an impairment of their in vivo invasive and metastatic capacities together with a higher susceptibility to in vitro apoptosis. Currently, the signaling mechanism of GPC3 is not clear. First, it was speculated that GPC3 regulates the insulin-like growth factor (IGF) signaling system. This hypothesis, however, has been strongly challenged. Recently, several reports indicated that at least in some cell types GPC3 serves as a selective regulator of Wnt signaling. Here we provide new data demonstrating that GPC3 regulates Wnt pathway in the metastatic adenocarcinoma mammary LM3 cell line. We found that GPC3 is able to inhibit canonical Wnt signals involved in cell proliferation and survival, as well as it is able to activate non canonical pathway, which directs cell morphology and migration. This is the first report indicating that breast tumor cell malignant properties can be reverted, at least in part, by GPC3 modulation of Wnt signaling. Our results are consistent with the potential role of GPC3 as a metastasis suppressor.

Mammalian Notum induces the release of glypicans and other GPI-anchored proteins from the cell surface.

Glypicans are heparan sulfate proteoglycans that are attached to the cell surface by a GPI (glycosylphosphatidylinositol)anchor. Glypicans regulate the activity of Wnts, Hedgehogs,bone morphogenetic proteins and fibroblast growth factors. In the particular case of Wnts, it has been proposed that GPI-anchored glypicans stimulate Wnt signalling by facilitating and/or stabilizing the interaction between Wnts and their cell surface receptors. On the other hand, when glypicans are secreted to the extracellular environment, they can act as competitive inhibitors of Wnt. Genetic screens in Drosophila have recently identified a novel inhibitor of Wnt signalling named Notum. The Wnt inhibiting activity of Notum was associated with its ability to release Dlp [Dally (Division abnormally delayed)-like protein; a Drosophila glypican] from the cell surface by cleaving the GPI anchor. Because these studies showed that the other Drosophila glypican Dally was not released from the cell surface by Notum,it remains unclear whether this enzyme is able to cleave glypicans from mammalian cells. Furthermore, it is also not known whether Notum cleaves GPI-anchored proteins that are not members of the glypican family. Here, we show that mammalian Notum can cleave several mammalian glypicans. Moreover, we demonstrate that Notum is able to release GPI-anchored proteins other than glypicans. Another important finding of the present study is that,unlike GPI-phospholipase D, the other mammalian enzyme that cleaves GPI-anchored proteins, Notum is active in the extracellular environment. Finally, by using a cellular system in which GPC3 (glypican-3) stimulates Wnt signalling, we show that Notum can act as a negative regulator of this growth factor.

Identification of diterpenoid compounds that interfere with Fli-1 DNA binding to suppress leukemogenesis.

The ETS transcription factor Fli-1 controls the expression of genes involved in hematopoiesis including cell proliferation, survival, and differentiation. Dysregulation of Fli-1 induces hematopoietic and solid tumors, rendering it an important target for therapeutic intervention. Through high content screens of a library of chemicals isolated from medicinal plants in China for inhibitors of a Fli-1 transcriptional reporter cells, we hereby report the identification of diterpenoid-like compounds that strongly inhibit Fli-1 transcriptional activity. These agents suppressed the growth of erythroleukemic cells by inducing apoptosis and differentiation. They also inhibited survival and proliferation of B-cell leukemic cell lines as well as primary B-cell lymphocytic leukemia (B-CLL) isolated from 7 patients. Moreover, these inhibitors blocked leukemogenesis in a mouse model of erythroleukemia, in which Fli-1 is the driver of tumor initiation. Computational docking analysis revealed that the diterpenoid-like compounds bind with high affinity to nucleotide residues in a pocket near the major groove within the DNA-binding sites of Fli-1. Functional inhibition of Fli-1 by these compounds triggered its further downregulation through miR-145, whose promoter is normally repressed by Fli-1. These results uncover the importance of Fli-1 in leukemogenesis, a Fli-1-miR145 autoregulatory loop and new anti-Fli-1 diterpenoid agents for the treatment of diverse hematological malignancies overexpressing this transcription factor.

Dok-R mediates attenuation of epidermal growth factor-dependent mitogen-activated protein kinase and Akt activation through processive recruitment of c-Src and Csk.

Dok-R has previously been shown to associate with the epidermal growth factor receptor (EGFR) and become tyrosine phosphorylated in response to EGF stimulation. The recruitment of Dok-R to the EGFR, which is mediated through its phosphotyrosine binding (PTB) domain, results in attenuation of mitogen-activated protein kinase (MAPK) activation. Dok-R's ability to attenuate EGF-driven MAPK activation is independent of its ability to recruit rasGAP, a known attenuator of MAPK activity, suggesting an alternate Dok-R-mediated pathway. Herein, we have determined the structural determinants within Dok-R that are required for its ability to attenuate EGF signaling and to associate with c-Src and with the Src family kinase (SFK)-inhibitory kinase, Csk. We demonstrate that Dok-R associates constitutively with c-Src through an SH3-dependent interaction and that this association is essential to Dok-R's ability to attenuate c-Src activity and diminish MAPK and Akt/PKB activity. We further illustrate that EGF-dependent phosphorylation of Dok-R requires SFK activity and, more specifically, that SFK-dependent phosphorylation of tyrosine 402 on Dok-R facilitates the inducible recruitment of Csk. We propose that recruitment of Csk to Dok-R serves to bring Csk to c-Src and down-regulate its activity, resulting in a concomitant attenuation of MAPK and Akt/PKB activity. Furthermore, we demonstrate that Dok-R can abrogate c-Src's ability to protect the breast cancer cell line SKBR3 from anoikis and that an association with c-Src and Csk is required for this activity. Collectively these results demonstrate that Dok-R acts as an EGFR-recruited scaffolding molecule that processively assembles c-Src and Csk to attenuate signaling from the EGFR.

Novel flavagline-like compounds with potent Fli-1 inhibitory activity suppress diverse types of leukemia.

E26 transformation-specific (ETS) gene family contains a common DNA-binding domain, the ETS domain, responsible for sequence-specific DNA recognition on target promoters. The Fli-1 oncogene, a member of ETS gene family, plays a critical role in hematopoiesis and is overexpressed in diverse hematological malignancies. This ETS transcription factor regulates genes controlling several hallmarks of cancer and thus represents an excellent target for cancer therapy. By screening compounds isolated from the medicinal plant Dysoxylum binectariferum in China, we identified two chemically related flavagline-like compounds including 4'-demethoxy-3',4'-methylenedioxyrocaglaol and rocaglaol that strongly inhibited Fli-1 transactivation ability. These compounds altered expression of Fli-1 target genes including GATA1, EKLF, SHIP1, and BCL2. Consequently, the flavagline-like compounds suppressed proliferation, induced apoptosis, and promoted erythroid differentiation of leukemic cells in culture. These compounds also suppressed erythroleukemogenesis in vivo in a Fli-1-driven mouse model. Mechanistically, the compounds blocked c-Raf-MEK-MAPK/ERK signaling, reduced phosphorylation of eukaryotic translation initiation factor 4E (eIF4E), and inhibited Fli-1 protein synthesis. Consistent with its high expression in myelomas, B-cell lymphoma, and B chronic lymphocytic leukemia (B-CLL), pharmacological inhibition of Fli-1 by the flavagline-like compounds or genetic knock-down via shRNA significantly hindered proliferation of corresponding cell lines and patients' samples. These results uncover a critical role of Fli-1 in growth and survival of various hematological malignancies and point to flavagline-like agents as lead compounds for the development of anti-Fli-1 drugs to treat leukemias/lymphomas overexpressing Fli-1.

Immunohistochemical study of glypican 3 in thyroid cancer.

In 123 patients with thyroid cancer, expression of glypican 3 (GPC3) was immunohistochemically investigated in tissue samples and the biological significance of GPC3 in thyroid cancer was examined. GPC3 was scarcely expressed in the normal thyroid gland, but was dramatically enhanced in certain types of cancers: 100% in follicular carcinoma (20/20 cases) and 70% in papillary carcinoma (48/69 cases). Expression of GPC3 in follicular carcinoma was significantly higher than that of follicular adenoma (p < 0.0019). In contrast, GPC 3 was not expressed in 17 cases of anaplastic carcinoma. A high expression of GPC3 mRNA was confirmed in cancer lesions, which were strongly positive for immunohistochemical staining. In 69 cases of papillary carcinoma, GPC3 was expressed at an early stage, suggesting that GPC3 expression in thyroid cancer is an early event in developing papillary carcinoma. Further studies are required to determine biological functions and molecular mechanisms underlying the upregulation of GPC3 in thyroid cancer.

Glypican-3 promotes the growth of hepatocellular carcinoma by stimulating canonical Wnt signaling.

Glypican-3 (GPC3) is a heparan sulfate proteoglycan that is bound to the cell membrane by a glycosyl-phosphatidylinositol anchor. GPC3 is expressed by most hepatocellular carcinomas but not by normal hepatocytes and benign liver lesions. We report here that GPC3 stimulates the in vitro and in vivo growth of hepatocellular carcinoma cells by increasing autocrine/paracrine canonical Wnt signaling. Co-immunoprecipitation experiments showed that GPC3 is able to form complexes with Wnts, and cell-binding assays indicated that GPC3-expressing cells have an increased capacity to bind Wnt. Collectively, these results suggest that GPC3 stimulates Wnt activity by facilitating the interaction of this polypeptide with its signaling receptors. Surprisingly, in contrast to the current model that proposes that Wnt-glypican binding is mediated by the heparan sulfate chains, we found that the nonglycanated GPC3 core protein can form complexes with Wnts. Furthermore, we showed that the glycosaminoglycan chains are not required for the stimulatory effect on Wnt signaling and hepatocellular carcinoma growth.